Summary

Merlin: A sad recluse, 100 years of age and still waiting for his other half to return.The Doctor: A strange man with stranger clothes, likes to talk. Has also lost a loved one, unfortunately she can’t return (or can she?)Merlin learns of a new threat to Albion... Aliens.

Basically the Doctor shows up in Medieval Britain and helps Merlin out of a rough spot (100 year depression). When he leaves, Merlin has another purpose. He’s not going to sit around moping as he waits for Arthur, he’s gonna live a little and protect his home.